1. Field of the Invention
This invention relates to an image forming apparatus using an electrophotographic method or an electrostatic recording method, for example, a copier, a printer, or a facsimile, and more particularly, to an image forming apparatus having a cleaning apparatus.
2. Description of the Related Art
Along with growth of the information society, there is a growing demand for an image forming apparatus (e.g. electrophotographic copier, electrophotographic printer) which forms images with higher speed, which requires less space, which generates high quality images, and which has an extensive longevity. Along with this growing demand, there is a demand for an electrophotographic image carrier used for an image forming apparatus which responds at high speed, which has a small size, and which provides high endurance. Accordingly, an image carrier applied with amorphous-Si, or an organic image carrier having an organic coat layer added with an inorganic material, for example, have been proposed for increasing longevity of the image carrier.
Since a cleaning apparatus is liable to damage the image carrier, a cleaning apparatus using a brush cleaning technique that allows toner remaining on the image carrier to be removed by electrostatic force has been proposed in order to prevent damage to the image carrier. However, the cleaning apparatus using the electrostatic method is unable to clean sufficiently since the cleaning apparatus relies on the polarity of the toner after transfer, and is largely influenced by environmental factors such as temperature and humidity. Accordingly, image quality cannot be improved with this method.
In addition, a higher image quality can be obtained the more the diameter of toner particles is reduced, and the more the shape of the toner particles becomes a sphere. Therefore, development and the market are directed toward providing toner particles with smaller diameters and with shapes closer to a sphere. Nevertheless, as the diameters of the toner particles become smaller and as the shapes of the toner particles become closer to a sphere, cleaning tends to become more difficult. More specifically, after a toner image is transferred to a target transfer body, it is difficult to sufficiently remove toner remaining on the surface of the image carrier, and thereby results in poor cleaning performance. Since toner, being situated at a contacting part between the image carrier and the cleaning blade, is more or less near a closest packed state during cleaning with a blade cleaning method, a first layer of toner, which is situated toward the image carrier side and which firmly adheres to the image carrier, slides against a second layer of toner situated above the first layer of toner, thereby causing the toner of the first layer to remain on the image carrier and resulting in poor cleaning performance.
In order to solve the foregoing problems, measures are taken for the cleaning blade method, for example, by increasing the degree of hardness of rubber and contact pressure of the blade. These, however, promote the wear of the image carrier and accelerate the wear of the rubber of the blade, thereby shortening the longevity of the cleaning blade.
Therefore, the cleaning blade is, for example, CVD (Chemical Vapor Deposition) coated with a film made of at least one kind of resin among a group comprising a styrene-based resin, an acryl-based resin, and an ethylene-based resin, as shown in Japanese Laid-Open Patent Application No. 2000-259051. By employing this technique of applying the CVD process to the cleaning blade, hydrolytic cleavage can be prevented, and the friction coefficient can be reduced.
As another example, in order to simplify assembly, Japanese Patent Registration No. 02961926 shows a cleaning blade having an elastic member disposed between a rubber plane fixing member for fixing a planar rubber member and a fixing member for fixing the entire cleaning blade. As another example, in Japanese Laid-Open Patent Application No. 9-325659, attachment holes and protruding parts are formed in a row-like arrangement, are engaged with each other, and are adhered to each other with an adhesive member.
As another example, Japanese Laid-Open Patent Application No. 11-219082 shows a cleaning blade having a layer structure, in which a resin layer is disposed on a metal plane.
As another example, Japanese Laid-Open Patent Application No. 11-30938 shows a cleaning apparatus having a cleaning blade including a free-end for cleaning the surface of the image carrier and a fixed-end for defining the position of a cleaning part during cleaning, and an ultra-sonic cleaning support device, disposed on the fixed-end of the cleaning blade, for floating off and removing the particles on the image carrier surface by applying vibration energy to the cleaning blade. With this example, vibration energy of a vibrator is concentrated toward the tip-end of the blade contacting the image carrier surface so that toner particles remaining on the image carrier surface may be floated off and prevented from adhering to the image carrier, therefore, enabling the cleaning blade to efficiently remove the floated off toner particles and provide a better cleaning performance.
As another example, Japanese Laid-Open Patent Application No. 11-174992 shows a cleaning blade provided with piezoelectric elements for applying vibration thereto, so that problems, for example, toner fusing upon the image carrier surface, abnormal noise, abnormal vibration, and peeling of the blade can be prevented from occurring.
A conventional cleaning process employing a cleaning blade for cleaning remaining toner faces problems such as turning over of the cleaning blade, generation of abnormal noise, and accelerated wear of the cleaning blade. Furthermore, the conventional cleaning process faces a problem of a filming phenomenon in which the blade member and the image carrier rubbing against each other causes resin material of toner to adhere to the surface of the image carrier. This results in degrading of image quality.
Furthermore, a cleaning method of applying vibrations to a cleaning blade is proposed in response to toners that are formed in smaller sizes and with more roundness. This method, however, faces a problem of wearing of the cleaning blade at a portion that rubs against the image carrier. Since the cleaning blade has less hardness than the image carrier, the cleaning blade wears faster than the image carrier, and has a shorter longevity than the image carrier.
In replacing a worn cleaning blade, the cleaning blade alone cannot be replaced, but needs to be replaced as a unit including, for example, a supporting member attached (adhered) to the cleaning blade.
That is, as in Japanese Patent Registration No. 02961926, since the components of the cleaning apparatus are all adhered to each other with an adhesive agent, the unit for replacing a worn cleaning blade would include other components adhered to the cleaning blade, to thereby increase cost. Furthermore, the example shown in Japanese Laid-Open Patent Application No. 9-325659, which has a plate spring member serving as an elastic member, is also unable to reduce cost, since the unit for replacing a worn cleaning would include the plate spring member.
Furthermore, in a case where a piezoelectric element, serving as a vibration source, is provided to the cleaning blade, the replacement of the cleaning blade requires further cost due to the additional cost of replacing the piezoelectric element. Particularly, when the piezoelectric element is still able to be used, the replacement of the cleaning blade is wasteful.
Meanwhile, in the example shown in Japanese Laid-Open Patent Application No. 2000-259051, since resin is coated on the surface of the cleaning blade by using a CVD method, an adhering property (effect) of rubber itself is reduced, to thereby degrade cleaning performance. Furthermore, the example has a problem of lacking endurance since the rubbing between the cleaning blade and the image carrier causes the coating on the blade surface to peel off. Even when a small portion of coating is peeled off, the rubbing causes the peeling to further spread around the peeled off portion, to thereby aggravate the lack of endurance.
In the example shown in Japanese Laid-Open Patent Application No. 11-219082, the plate-like blade member lacks cohesiveness with respect to the image carrier since the blade member is of a resin material. This causes creation of a gap therebetween, and results in poor cleaning performance. Furthermore, since the image carrier itself is formed of a resin mainly composed of polycarbonate, problems such as damaging of the surface therebetween are caused.
In the example shown in Japanese Laid-Open Patent Application No. 11-219082, environmental conditions, particularly temperature, cause large changes in the propagation of acoustic waves since standing waves are formed in a waveguide for propagating ultrasonic waves. This causes difficulty in obtaining a steady vibration. Furthermore, this example requires a considerably large vibrator for uniformly forming standing waves in a width direction of the image carrier, therefore making size reduction of the apparatus difficult. Furthermore, this example mainly focuses on reducing the adherence between the image carrier and the remaining toner particles, and the apparatus which applies vibration is not assigned to perform cleaning, but is a supplementary unit employed for cleaning.
In the example shown in Japanese Laid-Open Patent Application No. 11-174992, the waveform of the vibration applied to the cleaning blade is a standing wave, and is formed in the longitudinal direction of the cleaning blade. Accordingly, with this structure, vibration tends to be changed by external conditions in the environment. Furthermore, efficiency in the propagation of vibration is extremely poor since the material of the cleaning blade is an elastic material. Furthermore, since the vibration is applied in a longitudinal direction of the cleaning blade, the propagation of vibration is absorbed, thereby resulting in poor vibration efficiency.